Fuel burner control apparatus



FUEL BURNER CONTROL APPARATUS Filed Jail. 18, 1940 Albert-1' E. Bank Ultotngg Patented Apr. 11, 1944 FUEL BURNER coN'raoL APPARATUS Albert E. Baak, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application January 18, 1940, Serial No. 314,409

10 Claims. (Cl. 158-28) The present invention relates generally to apparatus for automatically controlling devices for feeding fuel to burners, and is particularly adapted to the control of oilburners.

One of the main objects of the invention is to provide a control apparatus which has a minimum number of parts and which is simple in operation.

Another object is to provide a control system in which a timer closes a control switch to render the fuel feeding'device operative, said switch being mechanically held closed by a combustion responsive device if combustion is established, otherwise the switch is reopened by said timer which moves out of cooperative relation with said switch. The switch is therefore under the direct control of said combustion responsive device on flame failure. 7 p y Another object of the invention is to provide the system witha normally closed safety switch which is carriedby the timer, and which is held open if combustion is not established during the return of the timer to its normal position. This prevents reenergization of the timer and the safety switch must be manually reset before the system can makeanother attempt to start. I

Still another object of the invention is to provide a control system in, which a timer closes a switch in control of a fuel feeding device, and in which an operating member, which has a slip frictional engagement with a combustion responsive device, holds the switch closed in the presence of combustion, and permits the switch to open and prevents reenergization of the timer in the case of failure to obtain combustion. Another object is to provide a system as described above wherein a single-pole double-throw switch is operated by the timer to simultaneously close the circuit in control of the fuel' feeding device and open another circuit to deenergize the timer.

These and otherv objectswill readily become apparent a the following specification is read in the light of the accompanying drawing in which the single figure shows in diagrammatical form a control system embodying the control device of my invention. '1 Referring to thedrawin g, the reference numeral ll indidates the timer which'is in the for'm of a bimetallic element fixed at itslower' end to the bracket l2 and 'adaptedto be heated, by

means of an electrical heater l3. The upper or free end of the timer carries afpairof'resilient blades l4 and I5 which carry themovablesafety switch contacts l6 and I1 and are sobiase'd that these contacts are normally in engagement with each other. The resilient blade l4, it will be noted, is electrically connected to the timer II and the blade I5 is insulated with respect to the blade l4 except when the contacts I6 and l! are in'engagement.

The upper end of the timer also carries an L shaped finger which, upon movement of the timer, is adapted to rotate the'lever 2| which is pivotally mounted as shown at 22. The lever 2| is adapted to actuate a switching mechanism indicated generally at 23. This switching mechanism is shown as a single-pole double-throw snap action switch of the self return type and although any switching mechanism of this type may be used, I prefer to employfthe switch shown in Figures 1 and 2 of mycopending application Serial No. 307,991, filed December '7, 1939, now Patent No. 2,318,734, issued May 11, 1943. This switch has been shown more or less diagrammatically and comprises a pivoted lever 24 carrying a pair of movable contacts 25' and 26 which are adapted to cooperate with stationary contacts 21 and 28, respectively. A leaf spring 29 acts through the toggle 30 on the upper end of the lever 24 to bias it for rotationlin a clockwise direction. The lever 24 is connected to a resilient operating arm 3| which in turn is engaged by an insulating pin 32. As the timer warps toward the left on being heated, it'rotates the lever 2| which in turn builds up a force in the resilient operating member 3| tending to rotate the lever 24 against the force exerted by the leaf spring 29. When the force built up in the member 3| is suflicient to initiate movement of the lever 24, the lever 24 snaps" to its actuated position in whichthe contacts 26 and 23 are in engagement and the contacts 25 and .21 are separated. This snap action-takes place as a result of the overcompensation of the spring rates of the operating member 3| and timer H by the change in angle between the toggle 30 and the lever 24. For a detailed explanation of this action, reference may be; had to my aforementioned copending; application, I I

A combustion responsive device which may take the form of a bimetallic element such as indicated at is placed eitherin the stack or in the combustion chamber where it may respond conveniently to the presence or absence of combustion within the furnace; This thermostat on being heated expands and 'moves'the rod 36 longitudinally toward the left, as seen in the drawing. An oper'ating member 31,'is'fmounted on the rod 38 and has a suitable slip irictioniengagement .IT to reclose. reclosed the system will make another attempt -until the reset lever 44 is rotated to lift the shoulder 45 out of engagement with the blade l4. allowing the safety switch contacts l6 and After the safety switch has been at a normal start.

One of the chief advantages of this system is that although the motor switch is closed by means of a timer, it is placed under the direct control of the combustion responsive thermostat once combustion has been established. When the system is in normal running condition the timer II will be in its cold position and the thermostat 35 will be expanded and will be holding the contacts 26 and 28 closed by means of the finger 39 which engages the lever 2|. If a flame failure should occur at this time the thermostat 35 will immediately begin to contract and withdraw the finger 39 toward the right permitting contacts 26 and 28 to open and shut down the humor motor and ignition device. At this time if the space thermostat is still calling for heat the original energizing circuit for the heater 13 will be reestablished and the timer II will be heated and after a predetermined time will reclose the contacts 26, 28 and open the contacts 25, 21. If combustion is established at this time,

the system will return to its normal running condition. If combustion is not established the thermostat 35 will not expand and the timer H as it returns to its cold position will after a predetermined time open the safety switch contacts l6 and i1 and the system will remain locked out until manual intervention. In other words, this system will recycle once following a flame failure.

It will therefore be seen that I have provided a simplified control system for fuel burners in which a timer closes the motor switch and in which the motor switch is held closed directly by a combustion responsive thermostat so that a quick shut-down may be obtained in case of a flame failure.

As many changes and modifications of this arrangement may occur to those who are skilled in the art I wish it to be understood that I am to be limited only by the scope of the appended claims and not by the specific embodiment disclosed.

I claim as my invention:

1. A fuel burner control device comprising in combination, a control switch for controlling an electrical fuel feeding device, a normally closed safety switch the opening of which prevents automatic operation of the system until manual intervention, a timer, means for energizing said timer, said timer first closing said control switch so as to energize an electrical fuel feeding device when electrically connected thereto, and a predetermined time thereafter Opening said safety switch to deenergize said electrical fuel feeding device, and means adapted to respond to combustion for preventing said timer from opening said safety switch and for maintaining said control switch mechanically disconnected from said timer if subjected to combustion conditions before the elapse of said predetermined time, said last mentioned means including a thermal element and mechanical conncetions between said thermal element and said control switch whereby the opening of said control switch upon said last named means being no longer subjected to combustion conditions is controlled directly by said thermal element independently of said timer and takes place without movement of said timer.

2. A fuel burner control system comprising in combination, an electrical fuel feeding device, a biased open switch, a biased closed switch, a timer which moves from a normal position on energization and back to said normal position on deenergization, a main switch, an energizing circuit for said timer including said main switch and said biased closed switch, said timer as a result of energization opening said biased closed switch and closing said biased open switch, closure of said biased open switch causing energization of said electrical fuel feeding device, a normally closed safety switch in control of the energizing circuit for said timer, opening of said biased closed switch causing deenergization of said timer which, a predetermined time thereafter, will open said safety switch and also permit said biased closed and biased open switches to return to closed and open positions respectively, and combustion responsive means having hot and cold positions, said combustion responsive means being operative to prevent the opening of said biased open switch and said safety switch if it moves to its hot position before the elapse of said predetermined time.

3. A fuel burner control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves from a normal position on energization and returns to said normal position on deenergization, a main switch for energizing said timer to close said control switch and hence energize said fuel feeding device, said timer deenergizingitself at substantially the same time and then reopening said control switch a predetermined time thereafter to deenergize said fuel feeding device, combustion responsive means for preventing, independently of the timer, the reopening of said control switch if combustion is established before the elapse of said predetermined time, a normally closed safety switch carried by said timer and controlling energization thereof, and a latch released by said timer on energization thereof, said latch opening said safety switch as said timer returns to its normal position, said combustion responsive means removing said latch. to prevent the opening of said safety switch upon the establishment of combustion.

4. A fuel burner control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which moves from a normal position on energization and returns to said normal position on deenergization, a main switch for energizing said timer to close said control switch and hence energize said fuel feeding device, said timer deenergizing itself at substantially the same time and then reopening said control switch a predetermined time thereafter to deenergize said fuel feeding device, a thermostat responsive to combustion, an operating member, a slip friction connection between said operating member and said thermostat, a safety switch carried by said timer and controlling the energization thereof, and a latch carried by said operating member, said latch resting on said safety switch when said timer is in its normal position, energization of said timer releasing said latch whereby on return of said timer to normal position said latch holds said safety switch open, said thermostat responding to combustion to prevent, independently of said timer, said control switch from opening, and raising said latch to prevent it from opening said safety switch, all if 5. An automatic control system comprising a burnermotor, a control switch therefor, a timer,

an energizing circuit therefor, a safety switch in said circuit, a second switch in said circuit, a main switch for establishing said energizing circult, said timer upon energization closing-said control switch and opening said second switch,

and on deenergization opening said safety switch, closing said second switch, and opening said control switch, thereby preventing reenergization of said timer and hence the reclosing of said control switch until after said safety switch has been ieclosed, and means responsive to combustion for holding said motor switch closed and preventing cuit, said timer upon energization closing said control switch and opening said second switch, and on deenergization opening said safety switch, closing said second switch, and opening said control switch, thereby preventing reenergization of said timer and hence the reclosing of said control switch until after said safety switch has been reclosed, and means responsive to combustion for holding said motor switch closed and preventing said timer from opening said safety switch it combustion is established first, said control switch and said second switch being in the form of a single pole double throw snap action switch, the common terminal of which is connected to said main switch.

'7. A fuel burner control system comprising. in combination, an electrical fuel feeding device, a control switch therefor, a timer which when energized closes said control switch and deenergizes itself, and upon deenergization normally causes said control switch to return to open position, a temperature responsive element subject to the heat of combustion, means transmitting a mechanical force from said element to said control "switch to prevent it from returning to open position in the event that combustion is established first, a safety switch, and means controlled by said combustion responsive element in the absence of combustion to cause said timer to open said safety switch as it returns to its deenergized position.

8. A fuel burner control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer which when energized closes said control switch and deenergizes itself, and upon deenergization normally causes said control switch to return to open position, a temperature responsive element subject to the heat of combustion, means transmitting a mechanical force from said element to said control switch to prevent it from returning to open position in the event that combustion is estabcombustion is established before theelapse of said predetermined time.

lishedfirst, a safety switch carried bysaidxtimer, anda latch positioned by said combustion responsive element in the absence of combustion so as toopen said safety switch assaidtimer returns to deenergized position, said latch being moved to inoperative position upon the establishment of combustion whereby. said safety switch remains closed as said timer returns to deenergized position.

9. A fuel burner control device comprising in combination, a control switch for controlling an electrical fuel feeding device, a timer positively associated in closing direction only with said switch and which when energized closes said control switch and deenergizes itself, said timer upon deenergization moving to a deenergized position, yieldable means tending to cause said control switch to return to open position as said timer moves to its deenergized position, a temperature responsive element adapted to besub- J'ected to the heat of combustion, means transmitting a mechanical force from said element to said control switch to hold it closed against the action of said yieldable means in the event that said temperature responsive element is subjected to the heat of combustion first without impeding the movement of said timer to its deenergized position, said temperature responsive element removing said mechanical force thereby releasing said control switch and permitting said yieldable means to return it toopen position upon said element subsequently being no longer subjected to the heat of combustion, and means actuated upon movement of said timer to energized position and back to deenergized position without said element being subjected to the heat of combustion to prevent the automatic reclosure of said control switch.

10. A fuel burner control system comprising in combination, an electrical fuel feeding device, a control switch therefor, a timer positively associated in closing direction only with said switch and which when energized closes said control switch and deenergizes itself, said timer upon deenergization moving to a deenergized position, yieldable means tending to cause said control switch to return to open positionas said timer moves. to its deenergized position, a temperature responsive element subject to the ,heat of combustion, means transmitting a mechanical force from said element to said control switch to hold it closed against the action of said yieldable means in the event that combustion is established first without impeding the movement of said timer to its deenergized position,said,temperature responsive element removing said. me chanical force thereby releasing said control switchand permittingsaid y'ieldablemeans to return it to open position upon a subsequent fal1 ure of combustion, and means actuated upon movement of saidtimer to energized position and .back todeenergized position without combustion 

